(1) Field of the Invention
The present invention relates to projectors having a function of automatically correcting distortion of images to be projected when projecting the images on a projection surface.
(2) Description of the Related Art
In recent years, use of projectors projecting still images and moving images on projection surfaces such as screens has been increased. When a projection surface has a non-planar shape or a planar shape not facing a projector, on the projection surface the projector projects an image having a shape different from a shape of an original of the image provided to the projector (hereinafter, referred to as an “original image”).
Therefore, in order to address the problem of distortion (deformation) of an image that is projected by a projector, various solutions as described below have been proposed to previously correct an original image to be projected and project the corrected image so that a user can view the projected image having almost the same shape as that of the original image.
One solution is disclosed in Japanese Unexamined Patent Application Publication No. 10-200836 (hereinafter, referred to as “Patent Reference 1”) to project an image having rectangular patterns on a projection surface and capture the projected image by a camera, when setting a projector and the projection surface. Then, an amount of distortion (hereinafter; referred to as a “distortion amount”) of the projected image is calculated from an outline of the patterned image captured by the camera, which is deformed to be a trapezium. Before an image to be actually viewed is projected, the image is previously processed to have distortion reversed from the calculated distortion amount so that the image can be projected without any distortion.
Another solution is disclosed in Japanese Unexamined Patent Application Publication No. 2001-83949 (hereinafter, referred to as “Patent Reference 2”) to project a test image illustrating dots (patterned image) on a projection surface and capture an image of the projected text image by a camera, when the projector and the projection surface are set. Next, by comparing an original of the test image to the image captured by the camera, a distortion amount of the projected test image is calculated. Then, before projecting an image to be actually viewed, the image is previously corrected to have distortion reversed from the calculated distortion amount so that images can be projected without distortion. In addition, Patent Reference 2 discloses a method of projecting such a test image by wavelength regions except a visual light range.
Still another solution is disclosed in Japanese Unexamined Patent Application Publication No. 2001-320652 (hereinafter, referred to as “Patent Reference 3”) to project a patterned image on a projection surface and capture an image of the projected image by a camera, when setting the projector and the projection surface. Then, by comparing the original patterned image to the image of the patterned image captured by the camera, a distortion amount of the projected patterned image is calculated. Then, before projecting an image to be actually viewed, the image is previously corrected to have distortion reversed from the calculated distortion amount so that images can be projected without distortion. It is also disclosed that the patterned image may illustrate a single dot, or a plurality of dots.
Still another solution is disclosed in Japanese Unexamined Patent Application Publication No. 2004-165944 (hereinafter, referred to as “Patent Reference 4”) to capture, using a camera, an image of an image projected by a projector on a projection surface, extract a feature point from an original image of the projected image, and extract, from the image captured by the camera, a corresponding point that corresponds to the feature point. Next, three-dimensional coordinates of corresponding points on the projection surface which correspond to the feature points are determined using (i) the feature points and the corresponding points and (ii) parameters of the projector and the camera. Then, the projected image is corrected using the three-dimensional coordinates. Patent Reference 4 also discloses that, in order to perform the correction, a planar surface of the projected image is divided to a plurality of triangular regions each having a vertex that is the feature point, and interpolate three-dimensional coordinates of a pixel in the triangular region from the three-dimensional coordinates of the vertex supposing that the triangular region were planar on three-dimensional space.
Still another solution is disclosed in Japanese Unexamined Patent Application Publication No. 2004-320662 (hereinafter, referred to as “Patent Reference 5”) to hold a predetermined approximation formula in a projector in order to correct distortion of images caused by a shape of a projection surface on which the images are projected. Then, when a user inputs a variable for the approximation formula, transformation (distortion correction) is performed depending on the shape of the projection surface. Patent Reference 5 discloses that the approximation formula is a parabola formula for cylindrical or spherical projection surfaces, a linear formula for wall-shaped projection surfaces having corners to correct the corners, and a formula of a trigonometric function for projection surfaces curving with sinusoidal patters.
Still another solution is disclosed in Japanese Unexamined Patent Application Publication No. 2006-94458 (hereinafter, referred to as “Patent Reference 6”) that a projector previously holds an approximation formula (function formula) regarding a shape of a projection surface. Then, when a user inputs a variable (variable parameter) for the approximation formula, a mesh model of the projection surface is generated, and distortion correction is performed based on a correspondence relationship between an input image (planar surface) and the mesh model of the projection surface.
Unfortunately, the above-described technologies have the following problems when a shape of the projection surface such as a screen or a positional relationship between the projection surface and the projector is changed in the middle of projecting the images.
The technology of Patent Reference 1 needs the projection of the patterned image and the calculation of the distortion amount, before projecting image(s) the user desires to view (hereinafter, is referred to as “viewing image(s)”). Therefore, if a shape of the projector surface or a positional relationship between the projection surface and the projector is changed in the middle of projection of viewing images, it is necessary to stop the projection and re-calculate a distortion amount by projecting a patterned image. Thus, the technology of Patent Reference 1 is not suitable for use in viewing moving images. Thus, the technology of Patent Reference 1 is not suitable for use in viewing moving images.
The technology of Patent Reference 2 also has the same problem as that of Patent Reference 1 when the patterned image illustrating dots. More specifically, if a shape of the projector surface or a positional relationship between the projection surface and the projector is changed in the middle of projection of viewing images, it is necessary to stop the projection and re-calculate a distortion amount by projecting a patterned image. Thus, the technology of Patent Reference 1 is not suitable for use especially in viewing moving image.
Here, the technology of Patent Reference 2 can solve the problem of Patent Reference 1 by projecting the patterned image in a range of wavelengths of light except visual light. This means that, even if a shape of the projector surface or a positional relationship between the projection surface and the projector is changed in the middle of projection of viewing images, it is possible to calculate a distortion amount without interrupting user's viewing of images. However, since the projector and the camera needs to handle images in the region of wavelengths of light except visual light, a cost related to hardware is increased.
The technology of Patent Reference 3 also has the same problem as that of Patent Reference 1 because a distortion amount is calculated using a patterned image. That is, if a shape of the projector surface or a positional relationship between the projection surface and the projector is changed in the middle of projection of viewing images, it is necessary to stop the projection and re-calculate a distortion amount by projecting a patterned image. Thus, the technology of Patent Reference 3 is not suitable for use in viewing moving images.
The technology of Patent Reference 4 can solve the problem of Patent Reference 1. Even if a shape of the projector surface or a positional relationship between the projection surface and the projector is changed in the middle of projection of viewing images, it is possible to calculate a distortion amount without interrupting user's viewing of images. However, a distance between feature points is approximated on a triangular planar surface in a three-dimensional space. Therefore, when the image illustrates a small number of feature points, a shape of the projection surface is approximated using large triangular planar surfaces, which results in a problem of unsatisfactory distortion correction. Furthermore, since approximation of a shape of the projection surface is decided using only feature points of an image, there is a possibility that the approximation is significantly varied depending on images. Therefore, when the calculation of a distortion amount of the projection surface using feature points in an image is performed (updated) every predetermined time interval (every several dozens of images, every few seconds, for example), projection of moving images consisting of quite different images that are projected continuously as time passes results in a possibility of a significant difference in an approximated shape of the projection surface between before and after the updating. This also results in changes in methods of correcting images, resulting in a possibility of causing discomfort of a user viewing projected images.
The technology of Patent Reference 5 can express a shape of the projection surface by an approximation formula, but details of the shape are expressed by obtaining a variable for the approximation formula which a user inputs. This means that before projecting viewing image(s) the user needs to set a variable, projecting a patterned image or the like and watching the projected image. In addition, in the same manner as disclosed in Patent Reference 1, if a shape of the projector or a positional relationship between the projection surface and the projector is changed in the middle of projection of viewing images, it is necessary to stop the projection and re-calculate a distortion amount by projecting a patterned image. Thus, the technology of Patent Reference 5 is not suitable for use in viewing moving images.
The technology of Patent Reference 6 can express a shape of the projection surface by an approximation formula, but details of the shape are expressed by obtaining a variable for the approximation formula which the user inputs. That is, before projecting viewing image(s) which the user desires to view, it is necessary to measure a shape or the like of the projection surface and then input a variable. In addition, in the same manner as disclosed in Patent Reference 1, if a shape of the projector surface or a positional relationship between the projection surface and the projector is changed in the middle of projection of viewing images, it is necessary to stop the projection and re-calculate a distortion amount by projecting a patterned image. Thus, the technology of Patent Reference 6 is not suitable for use in viewing moving images.
Thus, the present invention overcomes the problems of the conventional technologies as described above. It is an object of the present invention to provide a projector that can appropriately correct shapes of images projected on a projection surface without interrupting user's viewing of the projected image(s), even if a shape of the projector surface or a positional relationship between the projection surface and the projector is changed in the middle of the projection of the viewing images.